A Ser252Trp Mutation in Fibroblast Growth Factor Receptor 2 (FGFR2) Mimicking Human Apert Syndrome Reveals an Essential Role for FGF Signaling in the Regulation of Endochondral Bone Formation

Abstract

A S252W mutation of fibroblast growth factor receptor 2 (FGFR2), which is responsible for nearly two-thirds of Apert syndrome (AS) cases, causes retarded development of the skeleton and skull malformation resulting from premature fusion of the craniofacial sutures. We utilized a Fgfr2+/S252W mouse (a knock-in mouse model mimicking human AS) to demonstrate decreased bone mass due to reduced trabecular bone volume, reduced bone mineral density, and shortened growth plates in the long bones. In vitro bone mesenchymal stem cells (BMSCs) culture studies revealed that the mutant mice showed reduced BMSC proliferation, a reduction in chondrogenic differentiation, and reduced mineralization. Our results suggest that these phenomena are caused by up-regulation of p38 and Erk1/2 phosphorylation. Treatment of cultured mutant bone rudiments with SB203580 or PD98059 resulted in partial rescue of the bone growth retardation. The p38 signaling pathway especially was found to be responsible for the retarded long bone development. Our data indicate that the S252W mutation in FGFR2 directly affects endochondral ossification, resulting in growth retardation of the long bone. We also show that the p38 and Erk1/2 signaling pathways partially mediate the effects of the S252W mutation of FGFR2 on long bone development.

Fibroblast growth factor signaling in skeletal development and disease

“…This finding in mice supports the original observation in humans that Apert and Crouzon FGFR2 mutations cause increased osteoblast maturation and function in postnatal human suture development (Lomri et al 1998;Lemonnier et al 2001b;Tanimoto et al 2004;Baroni et al 2005;Marie 2015). FGFR2 mutations are also associated with increased osteoblast apoptosis in fused sutures in mice Chen et al 2014) and humans (Lemonnier et al 2001a;Lomri et al 2001;Kaabeche et al 2005); however, this appears to be a secondary event that occurs subsequent to osteoblast maturation and not the primary cause of the synostosis (Holmes et al 2009). Overall, the current literature indicates that the premature cranial ossification induced by FGFR2 mutations relates to an accelerated maturation of osteoblasts, whereas the moderate and transient increase in osteoprogenitor cell recruitment and the late osteoblast apoptosis do not appear to contribute primarily to the pathogenesis of the synostosis.…”

Genetic insights into the mechanisms of Fgf signaling

“…Treatment with a Mek inhibitor did not modify the skin or skull phenotypes in mutant mice (Wang et al 2012), suggesting that signaling through p38 but not Erk1/2 is required downstream from Fgfr2 Y394C during epidermal hyperplasia. Other studies have evaluated the requirement for specific signaling pathways during pathologic endochondral ossification in a mouse model of Apert syndrome (Yin et al 2008;Chen et al 2014a). Apert syndrome is caused by S252W-or P253R-activating mutations in FGFR2 and is characterized by craniosynostosis and syndactyly (Wilkie et al 1995).…”

“…Apert syndrome is caused by S252W-or P253R-activating mutations in FGFR2 and is characterized by craniosynostosis and syndactyly (Wilkie et al 1995). Fgfr2 S252W/+ and Fgfr2 P253R/+ mice are smaller than their wild-type counterparts, with decreased bone length and mass (Yin et al 2008;Chen et al 2014a). Both p38 and Erk1/2 activity was higher in bone mesenchyme stem cells derived from mutant mice, and inhibition of either pathway was capable of restoring normal length in cultured long bones (Yin et al 2008;Chen et al 2014a).…”

“…Fgfr2 S252W/+ and Fgfr2 P253R/+ mice are smaller than their wild-type counterparts, with decreased bone length and mass (Yin et al 2008;Chen et al 2014a). Both p38 and Erk1/2 activity was higher in bone mesenchyme stem cells derived from mutant mice, and inhibition of either pathway was capable of restoring normal length in cultured long bones (Yin et al 2008;Chen et al 2014a). The craniosynostosis associated with Apert syndrome is Erk1/2-dependent and can be prevented or treated using a Mek inhibitor (Shukla et al 2007;Yin et al 2008).…”

ESCRT-II/Vps25 Constrains Digit Number by Endosome-Mediated Selective Modulation of FGF-SHH Signaling

“…Interestingly, Vps25 ENU/ENU mutant hindlimbs exhibit Fgf4 expansion before Shh perturbations arise, which alone could result in enhanced proliferation and lack of cell death causing polydactyly. FGF signaling has also critical roles in the control of endochondral bone development (Chen et al, 2014; Ornitz and Marie, 2002). Notably, limbs of Vps25 ENU/ENU embryos display abnormally short and thick skeletal elements (Figures 2A,2B, S2F–S2L′), similar to humans with achondroplasia (dwarfism) (Ornitz and Marie, 2002).…”